Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

068
FXUS63 KLOT 090737
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
237 AM CDT Sat May 9 2026

.KEY MESSAGES...

- Warm, dry and breezy conditions this afternoon will result in
  an elevated risk for brush fires across northern Illinois.

- Cooler conditions Sunday into Monday, with the next chance for
  higher rain chances on Tuesday.

&&

.DISCUSSION...
Issued at 237 AM CDT Sat May 9 2026

In the very near term, the combination of light rain on Friday,
clearing skies early this morning, and ongoing weak moisture
advection has allowed for the development of shallow dense fog
across central Illinois. Southwest winds in excess of 20 knots
as low as 500 feet AGL will advect the fog and/or very low
stratus over the far southern CWA through daybreak. Any
fog/stratus should quickly erode after sunrise.

As a longwave trough centered over Hudson Bay remains nearly
stationary through the weekend, a small Pacific-based wave will
phase with a lobe from the longwave trough. The phased system
will rotate across the Great Lakes region, pushing a cold front
across the forecast area this afternoon.

The trough axis extending from the longwave trough is currently
evident on IR satellite as a band of mid-level cloud cover over
Wisconsin and far southeast Minnesota. Meanwhile, the faster
Pacific wave will overtake the lead trough late this afternoon
over or just east of the area. Expectations are for mid-level
showers to yield virga late morning into early afternoon before
potentially lowering and producing sporadic sprinkles or showers
at the surface. That said, nearly the entire area will remain
dry today.

Stout mixing, especially post-frontal, is expected this
afternoon amid decent dry-air advection. With the upstream
airmass characterized by dew points in the 20s, afternoon RH
values will likely fall to 30 percent or lower. At the same
time, low to mid-level flow will maximize over the area. While
there remains some question as to whether the stronger gradient
flow will be reflected all the way down to the surface, the deep
mixing should allow the deepest eddies to tap into the strong
flow (50 knots at 700 hPa) and produce a period of strong WNW/NW
gusts mid afternoon. Would not be surprised to see a high
sustained/gust ratio, with sustained winds under 20 mph and a
few of the highest gusts 35mph or higher. With the combination
of high winds, lower RH, and marginally low fine fuel moisture,
elevated brush fire conditions are possible across northern
Illinois for several hours this afternoon. Given the mild
weekend day and the expectation for a higher prevalence of
outdoor activities, will highlight messaging a bit more.

Yet another wave currently over Wyoming will quickly track
across central Illinois late this evening into the overnight
hours, yielding an axis of light rain across the far southern
CWA. Cooler and drier conditions are expected Sunday and Monday.
With high pressure nearing from the northwest and dry
conditions noted by PWATs under 0.3 inches, another unseasonably
chilly night with some patchy/areas of frost for outlying areas
is in store Sunday night. A Frost Advisory may be warranted for
interior portions of northern Illinois.

Broad ridging over the western CONUS will begin to edge
eastward next week. However, decent agreement with a stronger
trough (and rain/thunderstorm chances) digging southeastward
across the Great Lakes Tuesday into early Wednesday will likely
re-inforce, or at least slow the departure of, the long-standing
trough over eastern Canada. This will also likely dampen the
ridge and keep the warmest air to the south and west of the
area.

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1243 AM CDT Sat May 9 2026

Key messages:

- Increasingly gusty west-northwest winds this afternoon,
  possibly with some occasional gusts in excess of 30 kt after
  19Z.

- Winds abate by sunset early evening and turn northerly as a
  cold front moves across the area. There is also a small
  potential (~15% chance) that winds briefly shift northeast at
  the Chicago terminals with a lake breeze early this evening.

The gusty west-northwesterly winds expected in advance of an
approaching cold front this afternoon will be the primary
weather story/concern across the area terminals. While
gustiness up to 20 kt will begin to develop mid to late this
morning as the surface gradient begins to strengthen, it
appears even stronger wind gusts of at least 25-30 kt will
materialize this afternoon as deep diurnal boundary layer
mixing begins to top 10,000 feet AGL. Interestingly, westerly
winds at this level are expected reside in the 40-45 kt range
for a period mid to late this afternoon. Accordingly, the
potential for mixing down this higher momentum aloft does add
some concern for at least some sporadic higher gusts (perhaps
around, or a bit in excess of, 35 kt) at area terminals this
afternoon.

Winds will quickly abate early this evening and begin to turn
northerly around sunset as the surface cold frontal passage
occurs. While the winds may briefly shift more northeasterly
off the lake with the front early this evening, directions
should settle more northerly during the late evening and
overnight hours.

The main change for the 06Z TAFs was to hit the winds a bit
harder after 19Z this afternoon, going with west-northwesterly
gusts up around 28 kt through the late afternoon. We also
considered including a tempo group from 20-23Z for west-
northwesterly wind gusts up to 35 kt to account for the
some of the more sporadic strong gusts, but opted to hold off
for now. This mention may need to be added to the TAFs as
confidence increases.

Outside of the winds today, VFR conditions are expected, with
only some higher Level CIGs around 10,000 feet possible this
afternoon. A low (~20%) chance also exists for a few isolated
light showers or sprinkles this afternoon.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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